Water treatment residues curb phosphorus runoff

Residue from water-treatment plants, often discarded as waste into landfills, may make good soil treatments for preventing phosphorus runoff from farms.

Agricultural Research Service soil scientist Jeffrey M. Novak at the agency's Coastal Plains Soil, Water and Plant Research Center in Florence, S.C., is studying an alum-based water-treatment residual that increases soil's capacity to bond phosphorus, a vital plant nutrient.

The studies, done in collaboration with Ray Bryant, research leader at the ARS Pasture Systems and Watershed Management Research Unit in University Park, Pa., may benefit states along the nation's mid- to-southern-Atlantic seaboard, where sandy soils generally take up and hold less phosphorus than finer-textured soils.

Increased bonding, or adsorption, of phosphorus would curb runoff of this nutrient that can lower the oxygen content of water bodies and spoil the taste of drinking water. Phosphorus in manure makes agricultural facilities, such as large livestock production operations, potential sources of runoff pollution.

According to Novak, chemically binding phosphorus into water-insoluble complexes using residuals containing iron oxide, aluminum oxide and hydroxide may become an important management practice. The alum-based water-treatment residual this research focuses on has a high phosphorus-binding capacity.

A separate study, conducted on wheat by agronomist Eton Codling at the ARS Animal Manure and Byproducts Laboratory in Beltsville, Md., found that the treatment has no negative effect on plants' absorption of phosphorus once plant roots grow beyond the 6-inch-deep layer the treatment creates in soil.

In lab tests with sandy soil, the treatment increased phosphorus-binding potential four- to five-fold over that of untreated soil. The lab studies will be repeated, and additional research will be done in the field during the next two years. If successful, this use for waste from water-treatment processing not only could get rid of the waste, but would also hold phosphorus on the land until a crop uses it.

ARS is the U.S. Department of Agriculture's chief scientific research agency.